Dylann Roof, who pulled out a gun during a Bible study at Emanuel African Methodist Episcopal Church in Charleston on 17th June 2015, could be sentenced to death.
Forensic psychiatry specialist Dr James Ballenger deemed Roof in November to be competent, however, the court decided the proceedings were serious enough to warrant a second evaluation to ensure his mental state has not changed.
Roof was convicted by a federal jury on 15th December of all charges linked to the shootings, all the victims of whom were black.
Investigators said he planned the killings carefully and chose Emanuel African Methodist Episcopal Church in order to start a race war.
Roof's 33 federal convictions include nine counts of violating the Hate Crime Act resulting in death, three counts of violating the Hate Crime Act involving an attempt to kill and nine counts of obstruction of exercise of religion resulting in death.
They also include three counts of obstruction of exercise of religion involving an attempt to kill and use of a dangerous weapon, and nine counts of use of a firearm to commit murder during and in relation to a crime of violence.
Roof also is due to be tried on state murder charges, charges he could also be sentenced to death over.